医学免疫学英文版课件：Chapter 2Antigen

1、Chapter 13 Antigen Introduction1.Definitions of antigen Antigen: non-self substances which can combine with TCR or BCR or Ab and have the potential of inducing immune response . Antigen Tolerogen Allergen 2. Characters of Ag:ImmunogenicityAn ability of antigen which can stimulate the body to evoke a

2、 specific immune response(Ab or effect T cells).Antigenicity (Immunoreactivity)An ability of antigen which can combine with corresponding Ab or sensitized T lymphocyte. 3.Structure of antigenhapten and carrier Hapten: substances which can combine with Ab, but cannot induce immune response independen

3、tly. In another word, hapten only possess immunoreactivity.Carrier: enhance the immunogenicity of haptenComplete antigen :possess both functions Hapten +carrier -complete antigen Part I Immunogenicity and specificity of Ag I. Foreignness1. “Non-self ”substances:2. self component degeneration release

4、 of sequester antigen, eg, sperm, brain tissue , et al. According to Burnnet, Foreignness means substances which never contact with embronic lymphocytes. II. Specificityexist in both immunogenecity and immunoreactivity the basis of immunologic diagnosis and immunologic therapy1.Antigenic determinant

5、Antigen determiants (epitope) are small particular chemical groups of antigen which decide the specificity of the antigen.a subtle change of antigenic determinant (characteristics, number and conformation) can influence the specificity of Ag. protein antigen-5 residues Polysaccharide-6 residues Anti

6、gen determiant is the combining site of Ag and Ab2. Structrue of antigenic determinant*conformational determinant:-determinants composed of discontinuous residues by conformation-exist on the surface of Ag - recognized by B cell*sequential (or linear )determinant- determinants composed of continuous

7、 residues -exist in any where of Ag- recognized by T cell or B cell3. Functional determinate and sequester determinantFunctional determinate or Immunodominant groups (IDG) : epitope existed on the surface of Ag which can be recognized by BCR or combined with Ab easily.Sequester determinant: epitope

8、existed inside of Ag which can not be recognized by BCR or combined with Ab easily.degradationB/T Bactive4. Antigenic valence:total number of determinant which can be combined with Ab.5.T cell epitope and b cell epitope1) T cell epitopeAntigenic Determinants recognized by T cells(TCR)Composition:Pep

9、tidesSequential determinants(Exist in anywhere of Ag)ProcessedMHC presentation-Size8 -17 residues2)B cell epitopeAntigenic Determinants Recognized by B cells and AbComposition peptide, polysaccharides, nucleic acidsSequential determinants or Conformational determinants (existed on the surface of Ag)

10、Recognized directlyNo MHCSize5-7 residuesIII. Common antigen and cross reactionCommom antigen :different Ag own the same epitope or their epitope have similar structure,these epitopes are called common antigen.Cross reaction: reaction between the same Ab and different Ag with same similar determiant

11、s.mechanism of cross reaction -common Ag determinant -similar structure of Ag determinantsignificance: Because there are some common antigen determinants between different microbes, so the antiserum against one kind of Ag can also react with another Ag and couse a cross reaction . Part II. Factors i

12、nfluencing immune response of Ag 1.chemical and physical properties of Agchemical nature ProteinsPolysaccharides Nucleic Acids Lipids 2.Molecule weightreasonable large molecule( 10.0 kd) has good immuogenecity.more stationary more surface structure for lymphocyte to recognize3. Complexity of Ag stru

13、cture ring linear aromatic ring 4. conformation and accessibility 5.physical states : polymer monomerParticulate SolubleDenatured NativeII. Factors of bodyGenetics, Species:MHC Individual :Age, health, etc.III. Method of Administration Dose, Route(Subcutaneous Intravenous Intragastric), times,Adjuva

14、ntPart III. Classification of Agaccording to the need of T cellshelp when B cells produce Ab: TD-Ag (thymus dependent Ag) TI-Ag (thymus independent Ag)according to relative of Ag and body 1.according to the need of T cellshelp when B cells produce Ab:1) TD-Ag (thymus dependent Ag ): Ag which needs t

15、he help of T cell and Mwhen it stimulates B cell to produce Ab -most of TD-Ag are protein -more kinds of determinant, each number is less -composed of T and B cell epitopes -stimulate B cell to produce :IgG, IgM, IgA -capable of inducing CMI -immune memory 2) TI-Ag (thymus independent Ag) : Ag which

16、 can stimulate B cells to produce Ab without the help of T cell and M. -composed of repeated B cell epitopes -most are polysaccharide -there is more same repeat determinant -only induce B cell to produce IgM -can not induce CMI -no memoryThere are two kinds of TI-Ag(TI-1Ag and TI-2 Ag)TI-1Ag: compos

17、ed of repeated B cell epitopes and B cell mitogens can stimulate mature and immature B cells to produce Ab.TI-2Ag: composed of repeated B cell epitopes only can stimulate mature B cells to produce Ab only.2. according to relative: xenogenic antigen allogenic antigen autogenic antigen 1) allogenic an

18、tigen Ags comes from another species :Microbial Ag: Surface antigen “Vi” Ag Somatic Ag “O” Ag Flagellar Ag “H” Ag Pillus Ag Exotoxin and toxoid Exotoxin Produced by G+ bacteria Strong antigenicity and pathogenicity Toxoid Under suitable conditions, exotoxin loss its toxicity without affecting its an

19、tigenicity then the exotxoin turned into toxoid Immune serum of animal : animal serum contains Abs after immunized by some Ag has two properties : immnogenecity and immunoreactivity 2. Allogenic antigen Ags comes from different individuals of the same species.antigen of red blood cell (blood typing)

20、 :ABO system -very important in transfusion Rh systemHuman leukocyte antigen, HLA system -relate to transplantation -very important in immune regulation 3. Autogenic antigen Ags comes from self body1) Release of sequestered Ag2) Degeneration of proteinTumor antigenTumor specific Ag, TSA -only expres

21、s on the tumor cells but normal cellsTumor associated Ag,TAA -Its express is high on tumor cells but low on normal cells,eg. AFP CEA4.Heterophile Ag (forssman Ag):common Ags are shared by different species -no specificity of species - Significance : immunopathology DiagnosisPart IV.Superantigen and adjuvant1.Superantigen (SAg) :Antigens that can non-specifically stimulate a plenty of T/B cells and induce a very strong Ir with a extremely low concentration The mechanism of their action is different from t